Barcode and quick response (QR) codes can be encoded with information, and this information can be gleaned by reading the bar code or QR code with a reader. While bar codes and QR codes have historically been used on paper and other such substrates, with the advent of smart phones and other such devices, bar codes and QR codes can be stored, displayed, and read electronically. Consequently, bar codes, and QR codes in particular, can store a relatively large amount of digital information that can be optically communicated between common devices. Additionally, by using public-private key digital signatures on bar code and QR code content, authenticity can be established.